Tenascin is an extracellular matrix protein that is postulated to modulate tissue differentiation and cell migration during development. cDNA clones for tenascin were isolated from a cDNA library of adult porcine submaxillary glands. Three forms of tenascin clones were observed which varied with the number (8-10) of fibronectin type III (FN-III) domains. A major form consists of the N-terminal domain involved in the hexamer formation of tenascin subunits, 14 epidermal-growth-factor-like domains, nine FN-III domains, and the fibrinogen-like domain. A minor form with ten FN-III domains has never been described. Another striking feature is the lack of an RGD sequence that has been implicated to be crucial for cell adhesion, whereas RGD is present in both chicken and human tenascin sequences. In the adult, tenascin is expressed in very restricted tissues such as brain and chicken gizzard. A survey of tenascin transcripts in various adult rat normal tissues, including brain, revealed that the transcripts were detected only in submaxillary glands where tenascin expression has never been reported.